FKIE_CVE-2026-50538

Vulnerability from fkie_nvd - Published: 2026-08-21 21:16 - Updated: 2026-10-12 16:10
Severity
8.8 (High) - CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
Summary
LibVNCClient is a library for easy implementation of a VNC client. In versions 0.9.12 through 0.9.15, a malicious (or man-in-the-middle) VNC server can force a connecting `libvncclient` to write attacker-controlled data past the end of its framebuffer. This is an out-of-bounds heap write with attacker-controlled length, contents, and offset. It needs no authentication (the attacker is the server), works in a default build with default settings, and fires from a single `FramebufferUpdate` the moment the victim connects. It crashes any client unconditionally (denial of service); we also demonstrated it overwriting an application callback pointer and redirecting execution to attacker-chosen code (code execution) under the default configuration. Commit 540332be3e0acc566fa64da6f1b4680c72c724dd patches the issue.
References
security-advisories@github.comhttps://github.com/LibVNC/libvncserver/commit/540332be3e0acc566fa64da6f1b4680c72c724dd
security-advisories@github.comhttps://github.com/LibVNC/libvncserver/security/advisories/GHSA-v9pm-47h4-jcq8
134c704f-9b21-4f2e-91b3-4a467353bcc0https://github.com/LibVNC/libvncserver/security/advisories/GHSA-v9pm-47h4-jcq8
Impacted products
Vendor Product Version
To clipboard 

{
  "affected": [
    {
      "affectedData": [
        {
          "product": "libvncserver",
          "vendor": "LibVNC",
          "versions": [
            {
              "status": "affected",
              "version": "\u003e= 0.9.12, \u003c= 0.9.15"
            }
          ]
        }
      ],
      "source": "security-advisories@github.com"
    }
  ],
  "cveTags": [],
  "descriptions": [
    {
      "lang": "en",
      "value": "LibVNCClient is a library for easy implementation of a VNC client. In versions 0.9.12 through 0.9.15, a malicious (or man-in-the-middle) VNC server can force a connecting `libvncclient` to write attacker-controlled data past the end of its framebuffer. This is an out-of-bounds heap write with attacker-controlled length, contents, and offset. It needs no authentication (the attacker\nis the server), works in a default build with default settings, and fires from a single `FramebufferUpdate` the moment the victim connects. It crashes any client unconditionally (denial of service); we also demonstrated it overwriting an application callback pointer and redirecting execution to attacker-chosen code (code execution) under the default configuration. Commit 540332be3e0acc566fa64da6f1b4680c72c724dd patches the issue."
    },
    {
      "lang": "es",
      "value": "LibVNCClient es una biblioteca para la f\u00e1cil implementaci\u00f3n de un cliente VNC. En las versiones 0.9.12 a la 0.9.15, un servidor VNC malicioso (o man-in-the-middle) puede forzar a un \u0027libvncclient\u0027 que se conecta a escribir datos controlados por el atacante m\u00e1s all\u00e1 del final de su framebuffer. Esto es una escritura de heap fuera de l\u00edmites con longitud, contenido y desplazamiento controlados por el atacante. No necesita autenticaci\u00f3n (el atacante es el servidor), funciona en una compilaci\u00f3n predeterminada con configuraciones predeterminadas, y se activa desde una \u00fanica \u0027FramebufferUpdate\u0027 en el momento en que la v\u00edctima se conecta. Bloquea cualquier cliente incondicionalmente (denegaci\u00f3n de servicio); tambi\u00e9n demostramos que sobrescribe un puntero de callback de aplicaci\u00f3n y redirige la ejecuci\u00f3n a c\u00f3digo elegido por el atacante (ejecuci\u00f3n de c\u00f3digo) bajo la configuraci\u00f3n predeterminada. El commit 540332be3e0acc566fa64da6f1b4680c72c724dd corrige el problema."
    }
  ],
  "id": "CVE-2026-50538",
  "lastModified": "2026-10-12T16:10:00.220",
  "metrics": {
    "cvssMetricV31": [
      {
        "cvssData": {
          "attackComplexity": "LOW",
          "attackVector": "NETWORK",
          "availabilityImpact": "HIGH",
          "baseScore": 8.8,
          "baseSeverity": "HIGH",
          "confidentialityImpact": "HIGH",
          "integrityImpact": "HIGH",
          "privilegesRequired": "NONE",
          "scope": "UNCHANGED",
          "userInteraction": "REQUIRED",
          "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H",
          "version": "3.1"
        },
        "exploitabilityScore": 2.8,
        "impactScore": 5.9,
        "source": "security-advisories@github.com",
        "type": "Secondary"
      }
    ],
    "ssvcV203": [
      {
        "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
        "ssvcData": {
          "id": "CVE-2026-50538",
          "options": [
            {
              "exploitation": "poc"
            },
            {
              "automatable": "no"
            },
            {
              "technicalImpact": "total"
            }
          ],
          "role": "CISA Coordinator",
          "timestamp": "2026-08-24T19:39:31.246844Z",
          "version": "2.0.3"
        }
      }
    ]
  },
  "published": "2026-08-21T21:16:59.807",
  "references": [
    {
      "source": "security-advisories@github.com",
      "url": "https://github.com/LibVNC/libvncserver/commit/540332be3e0acc566fa64da6f1b4680c72c724dd"
    },
    {
      "source": "security-advisories@github.com",
      "url": "https://github.com/LibVNC/libvncserver/security/advisories/GHSA-v9pm-47h4-jcq8"
    },
    {
      "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
      "url": "https://github.com/LibVNC/libvncserver/security/advisories/GHSA-v9pm-47h4-jcq8"
    }
  ],
  "sourceIdentifier": "security-advisories@github.com",
  "vulnStatus": "Deferred",
  "weaknesses": [
    {
      "description": [
        {
          "lang": "en",
          "value": "CWE-122"
        },
        {
          "lang": "en",
          "value": "CWE-787"
        }
      ],
      "source": "security-advisories@github.com",
      "type": "Secondary"
    }
  ]
}



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